Driving support device and driving support method

ABSTRACT

In a driving support device for a vehicle, a collision prediction unit uses a determination plane defined by a lateral position axis indicating a position with respect to a vehicle in a lateral direction orthogonal to a vehicle traveling direction and a prediction time period axis indicating a time-to-collision set in the vehicle traveling direction. The collision prediction unit establishes a collision prediction area as an area in the determination plane. Further, the collision prediction unit determines whether at least a part of the section between both ends of a target is within the collision prediction area in the determination plane. Depending on the determination, the collision prediction unit predicts a collision with the target. The width of the collision prediction area along a lateral position axis is set based on the width of the vehicle. The lateral position of the collision prediction area is set based on a product between the speed of the target and the time-to-collision.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on Japanese Patent Application No.2015-254446, filed on Dec. 25, 2015, in the Japan Patent Office, theentire disclosure of which is hereby incorporated by reference herein.

BACKGROUND Technical Field

The present disclosure relates to a driving support device that ismounted to a vehicle to detect a target (object) ahead of the vehicleand causes the vehicle to perform driving support, and a driving supportmethod.

Background Art

In recent years, along with the advancement of sensors and dataprocessing, vehicles have been equipped with a driving support device toavoid collision accidents caused by the entry of a target into thetraveling direction of the vehicle from the lateral direction. Forexample, PTL 1 describes a driving support device that increases adetection area to detect a target when the lateral movement speed of thetarget approaching the vehicle from the lateral direction with respectto the traveling direction of the vehicle is equal to or higher than apredetermined speed and when the distance between the target and thevehicle is equal to or shorter than a predetermined distance. Thedetection area is within a range in which both a camera and a radar candetect the target, which makes it possible to detect the laterallymoving target with high accuracy.

CITATION LIST Patent Literature

[PTL 1] JP 2012-48460 A

As described above, the driving support device described in PTL 1increases the detection area according to the distance and speed of atarget when the target is approaching the vehicle from the lateraldirection with respect to the traveling direction of the vehicle,thereby to detect the target laterally approaching to the travelingdirection of the vehicle. However, when an object with large lateralwidth is approaching toward the traveling direction of the vehicle, thecentral position of the object used as the position of the object andthe range of presence of the object may become misaligned, andappropriate driving support may not be performed.

SUMMARY

A major objective of the present disclosure is to provide a drivingsupport device and a driving support method that make it possible to,even when a target with large lateral width is approaching toward thetraveling direction of the vehicle, determine a collision between thevehicle and the target with high accuracy.

A first aspect of the present disclosure is a driving support deviceincluding: a target detection unit that detects a target moving in adirection crossing the traveling direction of a vehicle; a collisionprediction unit that predicts a collision between the target detected bythe target detection unit and the vehicle; a support performing unitthat, when the collision prediction unit predicts a collision betweenthe target and the vehicle, causes the vehicle to perform drivingsupport for preventing the collision; a speed calculation unit thatcalculates the speed of the target; a time-to-collision calculation unitthat calculates a time-to-collision as a prediction time period untilthe occurrence of a collision between the target and the vehicle basedon information about the target detected by the target detection unit;and a both-ends detection unit that detects both ends of the targetdetected by the target detection unit in a direction orthogonal to thetraveling direction of the vehicle. The collision prediction unitestablishes a collision prediction area as an area in a determinationplane defined by a lateral position axis indicating a lateral positionwith respect to the vehicle in a lateral direction orthogonal to thetraveling direction of the vehicle and a prediction time period axisindicating the time-to-collision set in the traveling direction of thevehicle. The collision prediction unit predicts a collision with thetarget depending on whether at least a part of the section between bothends detected by the both-ends detection unit is within the collisionprediction area. The width of the collision prediction area along thelateral position axis is set based on the width of the vehicle. Thelateral position of the collision prediction area is set based on thespeed of the target calculated by the speed calculation unit and thetime-to-collision.

When the target detection unit detects a target moving in the directioncrossing the traveling direction of the vehicle, the both-ends detectionunit detects the both ends of the target in the direction orthogonal tothe traveling direction of the vehicle. The collision prediction area isestablished from the lateral position as the position of the targetrelative to the vehicle in the lateral direction orthogonal to thetraveling direction of the vehicle and the time-to-collision. The widthof the collision prediction area along the lateral position axis is setbased on the width of the vehicle. This makes it possible to determinethat a target present at a position exceeding the width along thelateral position axis is unlikely to collide with the vehicle. Inaddition, setting the lateral position of the collision prediction areabased on the speed of a target and the time-to-collision makes itpossible to predict with high accuracy whether the target moving at thecurrent speed is likely to collide with the vehicle. Further, acollision with the target is predicted depending on whether at least apart of the section between the both ends of the target detected by theboth-ends detection unit is within the collision prediction area.Accordingly, even when a target with large lateral width is approachingtoward the traveling direction of the vehicle, it is possible todetermine a collision between the vehicle and the target with highaccuracy. Moreover, it is possible to make an appropriate determinationon whether to perform the driving support.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features, and advantageous effects of thepresent disclosure will become clearer from the following detaileddescription with reference to the accompanying drawings. In thedrawings:

FIG. 1 is a set of block diagrams, in which part (a) thereof illustratesa block diagram of a hardware of a driving support device, and part (b)thereof illustrates a functional block diagram of a detection ECU,according to the present embodiment.

FIG. 2 is a diagram illustrating a problem that may occur under controlof a conventional detection ECU.

FIG. 3 is a diagram illustrating control performed by the detection ECUaccording to the present embodiment.

FIG. 4 is a flowchart of the control performed by the detection ECUaccording to the present embodiment.

FIG. 5 is a diagram illustrating an example of case where the collisionprediction area is corrected.

FIG. 6 a graph illustrating change tendencies of a correction value foruse in the correction of the collision prediction area.

FIG. 7 is a diagram illustrating an example of case where the collisionprediction area is corrected.

FIG. 8 is a diagram illustrating an example of case where the collisionprediction area is corrected.

FIG. 9 is a graph illustrating change tendencies of a correctioncoefficient for use in the correction of the collision prediction area.

FIG. 10 is a diagram illustrating an example of case where the collisionprediction area is corrected.

DESCRIPTION OF PREFERRED EMBODIMENTS

The driving support device according to the present embodiment ismounted to a vehicle (own vehicle) to detect a target around the ownvehicle, such as ahead of the own vehicle, and perform a driving supportcontrol. The driving support control serves as a PCS system (pre-crashsafety system) to avoid a collision with a target or reduce collisionaldamage.

Referring to part (a) of FIG. 1, a driving support device 100 includes adetection ECU (electronic control unit) 10 and a radar device 21, and animaging device 22.

The radar device 21 is a publicly known millimeter wave radar, forexample, that uses a high frequency signal in the millimeter waveband astransmission wave. The radar device 21 is disposed at the front end partof the own vehicle to detect the position of a target (called radardetection target) in an area at a predetermined detection angle astarget-detectable range. Specifically, the radar device 21 transmitssearch waves at predetermined intervals and receives reflected wavesfrom a plurality of antennas. The radar device 21 calculates thedistance to the radar detection target by the transmission time of thesearch waves and the reception time of the reflected waves. The radardevice 21 also calculates the relative speed (specifically, the relativespeed in the traveling direction of the vehicle) from the frequencies ofthe reflected wave from the radar detection target, which vary byDoppler Effect. In addition, the radar device 21 calculates the azimuthof the radar detection target from phase differences among the reflectedwaves received by the plurality of antennas. When the position andazimuth of the radar detection target can be calculated, the position ofthe radar detection target relative to the own vehicle (lateralposition) can be specified. Accordingly, the radar device 21 correspondsto a target detection unit and a speed calculation unit. The radardevice 21 transmits the search waves, receives the reflected waves, andcalculates the reflection positions and the relative speed at thepredetermined intervals, and transmits the calculated reflectionpositions and relative speed to the detection ECU 10.

The imaging device 22 is formed from, for example, a charged-coupleddevice (CCD) camera, a complementary metal-oxide semiconductor (CMOS)image sensor, a near-infrared camera, and others. In that case, theimage capture device 22 is mounted to a predetermined vertical positionof the own vehicle that is the center of the own vehicle in the lateraldirection to capture a bird's-eye-view image of a region increasing witha predetermined angular range ahead of the own vehicle. The imagingdevice 22 extracts a feature point indicating the presence of a target(called image detection target) in the captured image. Specifically, theimaging device 22 extracts edge points based on information aboutbrightness of the captured image, and applies a Hough transform to theextracted edge points. In the Hough transform, for example, points of astraight line where a plurality of edge points are continuously arrayed,or points of intersections between straight lines are extracted asfeature points. The imaging device 22 captures images and extracts afeature point, and transmits the results of extraction of the featurepoints to the detection ECU 10, at regular intervals. The imaging device22 may be a monocular camera or a stereo camera. In this way, the radardevice 21 and the imaging device 22 detect a target moving in thedirection crossing the traveling direction of the own vehicle.

The radar device 21 and the imaging device 22 are connected to thedetection ECU 10. The detection ECU 10 is a computer including a CPU(central processing unit) 11, a RAM (random access memory) 12, a ROM(read only memory) 13, and an I/O (input/output) (not illustrated), andothers. The detection ECU 10 performs these functions by the CPU 11executing a program installed on the ROM 13. In the present embodiment,the program installed in the ROM 13 is a determination program fordetermining whether the radar detection target and the image detectiontarget are identical based on the information about the radar detectiontarget and the information about the image detection target.

Specifically, the detection ECU 10 establishes a correlation between aradar-detection target position that is a position obtained from aradar-detection target and an image-detection target position that is afeature point obtained from an image-detection target. Specifically, ifthese positions are located close to each other, they are correlated toeach other as being based on an identical target. When the imagedetection target position is present in the vicinity of theradar-detection target position (in the present embodiment, the distancebetween the radar-detection target position and the image-detectiontarget position is within a predetermined range), there is a highprobability that the target is actually present at the radar-detectiontarget position. The state in which the position of the target can beaccurately acquired by the radar device 21 and the imaging device 22will be called a fusion state. For a target determined as in the fusionstate, the detection ECU 10 determines that the target is present atthat position.

Under the determination program installed on the ROM 13, whendetermining that the target is present at that position, the detectionECU 10 then determines whether to perform a prescribed driving supportprocess on guard against a collision with the target. The ROM 13corresponds to a non-transitory computer readable recording medium.Besides the ROM 13, the recording medium includes computer-readableelectronic media such as DVD-ROM (digital versatile disk read onlymemory), CD-ROM (compact disc read only memory), and hard disk. Asillustrated in part (b) of FIG. 1, the detection ECU 10 performs variousfunctions by a collision prediction unit 15, a support performing unit16, and a time-to-collision calculation unit 17.

In the present embodiment, the driving support process corresponds to awarning process which notifies the driver of a target ahead of the ownvehicle that may collide with the own vehicle and a braking processwhich is applied to brake to the own vehicle. Therefore, the own vehicleis equipped with a warning device 31 and a braking device 32 as safetydevices 30 that are driven under control demand from the detection ECU10.

The warning device 31 includes a speaker and a display mounted to theinterior of the own vehicle. When the detection ECU 10 determines that atime-to-collision (TTC) described later becomes shorter than a firstpredetermined time and the probability of a collision of the own vehiclewith a target becomes high, the warning device 31 outputs a warningsound, a warning message, or the like to notify the driver of the riskof a collision. Such a warning sound, a warning message, or the like isoutputted according to a control command from the detection ECU 10.Accordingly, the warning device 31 corresponds to a notification unit.

The braking device 32 is a device that serves as a brake for the ownvehicle. When the detection ECU 10 determines that the time-to-collisiondescribed later becomes shorter than a second predetermined time set tobe shorter than the first predetermined time, and the probability of acollision of the own vehicle with a target becomes high, the brakingdevice 32 is activated under a control command from the detection ECU10. Specifically, the braking device 32 enhances braking force derivedfrom a brake operation by the driver (brake assist function) orautomatically applies a brake if the driver does not perform a brakeoperation (automatic braking function). Accordingly, the braking device32 corresponds to an automatic braking unit.

The time-to-collision calculation unit 17 of the detection ECU 10calculates the time-to-collision as a time before the target willcollide with the own vehicle. Specifically, the time-to-collisioncalculation unit 17 calculates the time-to-collision based on therelative distance and relative speed of the target and the own vehicle.3 o As illustrated in FIG. 2, the time-to-collision calculation unit 17establishes an overlapping detection area in which an area where theradar device 21 can detect a target and an area where the imaging device22 can detect a target overlap in a determination plane. Thedetermination plane is defined by a longitudinal axis indicating thetime-to-collision (TTC), and a horizontal axis indicating the lateralposition of the target with respect to the own vehicle in the lateraldirection orthogonal to (crossing) the traveling direction of the ownvehicle.

However, not all targets present in the overlapping detection area havea risk of colliding with the own vehicle. Therefore, a target within acollision prediction area set to further limit the overlapping detectionarea is recognized as a target that may collide with the own vehicle. Inthe determination plane, the target is specified as a point (currentposition) by the lateral position and the time-to-collision. Asillustrated in the rectangular frame, it may be determined that a targetwithin a conventional collision prediction area established by settingthresholds for the lateral position and the time-to-collision is atarget that might collide with the own vehicle. As indicated by ahatched area, however, the area having a high probability of collisionwith the own vehicle is narrower than the collision prediction area.Accordingly, even when the target crosses the traveling direction of theown vehicle without contacting the own vehicle, or when the own vehiclepasses through the moving direction of the target before the entry ofthe target into the traveling direction of the own vehicle, the drivingsupport process may be performed although the target is within thecollision prediction area and there will be no collision between thetarget and the own vehicle.

Accordingly, the collision prediction unit 15 of the detection ECU 10according to the present embodiment sets the lateral position of thecollision prediction area based on the speed of the target present inthe overlapping detection area and the time-to-collision. Specifically,as illustrated in FIG. 3, the collision prediction unit 15 establishesthe collision prediction area in such a manner as to equalize the widthof the collision prediction area along the lateral axis with the widthof the own vehicle, and set the coverage of the collision predictionarea along the longitudinal axis from 0 to the first predetermined time.In this case, the speed of the target along the lateral position axis(positive on the rightward side) at time t is designated as V(t), andthe time-to-collision is designated as TTC. Therefore, right end Xr(t)and left end Xl(t) of the collision prediction area are expressed byEquations (1) and (2). The own vehicle front right end Xr expressed inthe equation indicates the coordinate position of a point shiftedrightward from the center of the own vehicle by half the vehicle widthalong the lateral position axis. The own vehicle front left end Xlexpressed in the equation indicates the coordinate position of a pointshifted leftward from the center of the own vehicle by half the vehiclewidth along the lateral position axis. Accordingly, it is possible toset a target that will pass through the own vehicle so that it is notincluded within the collision prediction area, and determine that atarget present in the collision prediction area may collide with the ownvehicle and perform the driving support process to prevent a collisionbetween the target and the own vehicle.

Xr(t)=Xr−V(t)×TTC  (1)

Xl(t)=Xl−V(t)×TTC  (2)

In the present embodiment, the target is assumed to be a bicycle. Thebicycle is a target that is long in length along the lateral positionaxis. Accordingly, depending on the situation, the central part of thebicycle along the lateral position axis may not be included in thecollision prediction area, but a part of the bicycle might enter thecollision prediction area (see FIG. 2). In such a situation, when thebicycle as the target is specified as a point by the lateral positionand the time-to-collision in the determination plane, the drivingsupport process cannot be performed properly, and the target and the ownvehicle may collide with each other.

To prevent this, the collision prediction unit 15 acquires positioninformation from the image captured by the imaging device 22. Theposition information relates to both ends of the target along thelateral axis in the determination plane. Accordingly, in the presentembodiment, the imaging device 22 corresponds to a both-ends detectionunit. As illustrated in FIG. 3, when at least a part of the sectionbetween the acquired both ends is within the collision prediction area,the collision prediction unit 15 determines that the target may collidewith the vehicle, and thus recognizes the target as a target of thedriving support process.

Specifically, the collision prediction unit 15 acquires from the imagecaptured by the imaging device 22, lateral position information aboutthe left end of the target (target left end ObjL) and lateral positioninformation about the right end of the target (target right end ObjR),with respect to the traveling direction of the vehicle. In addition, thecollision prediction unit 15 calculates the right end Xr(t) of thecollision prediction area at the time to collision with the targetcalculated by Equation (1), and the left end Xl(t) of the collisionprediction area at the time to collision with the target calculated byEquation (2). Then, as expressed in Equation (3), the collisionprediction unit 15 determines whether the following relationship isestablished in the determination plane. Specifically, the relationshipis that the lateral position of the target right end ObjR is larger thanthe lateral position of the left end Xl(t) of the collision predictionarea at the calculated time-to-collision, and the lateral position ofthe right end Xr(t) of the collision prediction area at the calculatedtime-to-collision is larger than the lateral position of the target leftend ObjL. The target satisfying the relationship of Equation (3) is atleast partially included in the collision prediction area. That is, evenif a target with large lateral width is approaching toward the travelingdirection of the vehicle, it is possible to determine a collisionbetween the vehicle and the target with high accuracy.

$\begin{matrix}\left\lbrack {{Equation}\mspace{14mu} 1} \right\rbrack & \; \\{{AND}\left\lbrack \begin{matrix}{{{Xl}(t)} \leq {ObjR}} \\{{Objl} \leq {X_{r}(t)}}\end{matrix} \right.} & (3)\end{matrix}$

In the present embodiment, the support performing unit 16 of thedetection ECU 10 performs the driving support control described laterwith reference to FIG. 4. When the collision prediction unit 15 predictsthat the target and the own vehicle will collide with each other, thesupport performing unit 16 causes the vehicle to perform the drivingsupport to prevent the collision. The detection ECU 10 repeatedlyperforms the driving support control described in FIG. 4 atpredetermined intervals while the power supply for the detection ECU 10is on.

First, in step S100, the detection ECU 10 determines whether thedistance between the radar detection target and the image detectiontarget is within a predetermined range in the overlapping detectionarea. When the distance between the radar detection target and the imagedetection target is not within the predetermined range in theoverlapping detection area (NO at S100), the detection ECU 10 terminatesthe present control. When the distance between the radar detectiontarget and the image detection target is within the predetermined rangein the overlapping detection area (YES at S100), the detection ECU 10determines that an identical target has been detected, and proceeds tostep S110.

In step S110, the detection ECU 10 acquires from the radar device 21 therelative position, the relative distance, and the relative speed of thetarget determined as identical target. In this case, the relativeposition of the target is specified based on the position and azimuth ofthe target with respect to the own vehicle, which corresponds to thelateral position of the target in the determination plane. The relativedistance corresponds to the distance between the own vehicle and thetarget calculated based on the relative position. The detection ECU 10also acquires the position information about the both ends of the targetfrom the image captured by the imaging device 22. In step S120, thetime-to-collision calculation unit 17 calculates the time-to-collisionwith the target from the relative speed and relative distance of thetarget acquired from the radar device 21. In step S130, the collisionprediction unit 15 establishes the collision prediction area in thedetermination plane, based on the information about the target acquiredin steps S110 and S120.

In step S140, the detection ECU 10 determines whether at least a part ofthe target is within the collision prediction area established in stepS130. When it is determined that the target is not within the collisionprediction area (NO at S140), the detection ECU 10 terminates thepresent control. When it is determined that at least a part of thetarget is within the collision prediction area (YES at S140), thedetection ECU 10 proceeds to step S150 where the support performing unit16 causes the warning device 31 to perform the notification process.

In step S160, the detection ECU 10 determines whether the time tocollision with the target is shorter than the second predetermined time.When it is determined that the time to collision with the target islonger than the second predetermined time illustrated in FIG. 7 (NO atS160), the detection ECU 10 terminates the present control. When it isdetermined that the time to collision with the target is shorter thanthe second predetermined time (YES at S160), the detection ECU 10proceeds to step S170 where the support performing unit 16 causes thebraking device 32 to perform the automatic braking control, and thenterminates the present control.

According to the aforementioned configuration, the present embodimentprovides the advantageous effects described below.

The width of the collision prediction area along the lateral positionaxis is set based on the width of the own vehicle. This makes itpossible to determine that a target is present at a position exceedingthe width along the lateral position axis is unlikely to collide withthe own vehicle. In addition, setting the lateral position of thecollision prediction area based on the speed of a target and thetime-to-collision makes it possible to determine with high accuracywhether the target approaching at the current speed is likely to collidewith the own vehicle. Further, when the right end Xr(t) and left endXl(t) of the time to collision with the target calculated according toEquations (1) and (2) and the lateral positions of the both ends of thetarget (the target left end ObjL and target right end ObjR) satisfy therelationship in Equation (3), it can be predicted that at least a partof the target will collide with the own vehicle. Accordingly, even whena target having a large lateral width is approaching toward thetraveling direction of the own vehicle, it is possible to determine acollision between the own vehicle and the target with high accuracy.Moreover, it is possible to appropriately determine whether to performthe driving support.

The lateral position of the collision prediction area is set by straightlines with the speed of the target as slopes as described in Equations(1) and (2). Therefore, it is possible to draw in the determinationplane, a virtual line of the right end Xr(t) of the collision predictionarea determined by Equation (1), and a virtual line of the left endXl(t) of the collision prediction area determined by Equation (2). Thesevirtual lines are boundary lines in the case where the target running atthe current speed collides with the own vehicle. Accordingly,establishing the collision prediction area based on these virtual linesmakes it possible to determine that a target passing by the own vehiclewithout a collision is outside the collision prediction area.

The following modifications may be made to the above embodiment.

In the aforementioned embodiment, the target is assumed to be a bicycle.In this regard, the target is not limited to a bicycle but may be apedestrian, a motorcycle, or an automobile, for example.

The aforementioned embodiment includes the means for preventing acollision between the own vehicle and the target present in thecollision prediction area according to the time to collision with thetarget. Specifically, the warning device 31 is activated when at least apart of the target is present in the collision prediction area.Additionally, when the braking device 32 is activated when the time tocollision with the target present in the collision prediction area isshorter than the second predetermined time. In this regard, the meansfor preventing a collision with the target are not limited to thewarning device 31 and the braking device 32. For example, instead of theautomatic braking control by the braking device 32, a steering wheelcontrol unit may be provided so that, when it is determined that thetime to collision with the target present in the collision predictionarea is shorter than a third predetermined time, the steering wheel canbe automatically controlled to avoid a collision with the target. Thethird predetermined time is set as a time necessary for safely avoidinga collision with the target by the automatic control of the steeringwheel, for example.

In the aforementioned embodiment, the fusion determination is made usingthe radar device 21 and the imaging device 22. In this regard, thefusion determination need not necessarily be made to perform the drivingsupport control. However, a driving support device not including theimaging device 22 but including only the radar device 21 may perform thedriving support control. In this case, the radar device 21 is caused toacquire the position information about both ends of the target in thedetermination plane. In another example, therefore, the radar device 21corresponds to the both-ends detection unit.

Example 1

In the aforementioned embodiment, the fusion determination is made usingthe radar device 21 and the imaging device 22. In this regard, thefusion determination need not necessarily be made to perform the drivingsupport control. However, a driving support device including the imagingdevice 22 but not including the radar device 21 may perform the drivingsupport control. In this case, the driving support device is caused todetect the position and speed of the target from the image captured bythe imaging device 22. In Example 1, therefore, the imaging device 22corresponds to the speed calculation unit.

However, when the speed of a target is detected from the image capturedby the imaging device 22, the large part of the image is occupied by thetarget near the own vehicle, and thus there is a risk that the speed ofthe target might be incorrectly calculated as being lower than actualone. In this case, it may be incorrectly determined that the target isnot within the collision prediction area due to the error in the speedof the target, although the target actually is within the collisionprediction area.

Accordingly, when the relative distance between the own vehicle and thetarget is shorter than a first predetermined distance, the collisionprediction unit 15 corrects the collision prediction area to be wider inthe lateral direction such that the straight line of the right end Xr(t)of the collision prediction area has a larger slope and the straightline of the left end Xl(t) of the collision prediction area has asmaller slope, as illustrated in FIG. 5. Specifically, as described inEquation (4), the slope of the straight line of the right end Xr(t) ofthe collision prediction area is corrected by multiplying the product ofthe speed of the target and the time-to-collision by a value calculatedby adding a first correction value α to 1. In addition, as described inEquation (5), the slope of the straight line of the left end Xl(t) ofthe collision prediction area is corrected by multiplying the product ofthe speed of the target and the time-to-collision, by a value calculatedby subtracting the first correction value α from 1. As illustrated inFIG. 6(a), the first correction value α is 0 when the relative distanceis longer than the first predetermined distance, and tends to be largerthan 0 when the relative distance becomes shorter than the firstpredetermined distance. This allows the target to be included within thecollision prediction area even if an error has occurred in the speed ofthe target calculated using the image captured by the imaging device 22.The slope of the straight line of the right end Xr(t) of the collisionprediction area is corrected.

Xr(t)=Xr−V(t)×TTC×(1+α)  (4)

Xl(t)=Xl−V(t)×TTC×(1−α)  (5)

In Example 1, the slope of the straight line of the right end Xr(t) ofthe collision prediction area and the slope of the straight line of theleft end Xl(t) of the collision prediction area are corrected. In thisregard, both the slopes of the straight lines need not necessarily becorrected by using the first correction value α. For example, whencorrecting the slope of the straight line of the right end Xr(t) of thecollision prediction area, the first correction value α may be used towiden the collision prediction area in the lateral direction.Conversely, the slope of the straight line of the left end Xl(t) of thecollision prediction area need not be corrected or may be correctedusing a value different from the first correction value α.

Example 2

In the aforementioned embodiment, the width of the collision predictionarea along the lateral axis is set to the width of the own vehicle. Inthis regard, in the collision prediction area in a range in which thetime-to-collision is longer than a fourth predetermined time, asillustrated in FIG. 7, the collision prediction unit 15 narrows thewidth of the collision prediction area along the lateral axis bycorrecting the slope of the straight line of right end Xr(t) of thecollision prediction area to be smaller, and correcting the slope of thestraight line of left end Xl(t) of the collision prediction area to belarger. The fourth predetermined time is set to be longer than thesecond predetermined time and shorter than the first predetermined time.Specifically, as described in Equation (6), the slope of the straightline of the right end Xr(t) of the collision prediction area iscorrected by multiplying a value calculated by subtracting a secondcorrection value β from 1, by the product of the speed of the target andthe time-to-collision. In addition, as described in Equation (7), theslope of the straight line of the left end Xl(t) of the collisionprediction area is corrected by multiplying a value calculated by addingthe second correction value β to 1, by the product of the speed of thetarget and the time-to-collision. The second correction value β is 0when the time-to-collision is shorter than the fourth predeterminedtime, and tends to be larger than 0 when the time-to-collision becomeslonger than the fourth predetermined time, as illustrated in FIG. 6(b).

Xr(t)=Xr−V(t)×TTC×(1−β)  (6)

Xl(t)=Xl−V(t)×TTC×(1+β)  (7)

It is predicted that the target detected in the range where thetime-to-collision is longer than the fourth predetermined time will taketime to collide with the own vehicle, and the target or the own vehiclemight accelerate or decelerate from this time forward. Therefore, eventhough the target and the own vehicle are currently on collision paths,these paths may change hereafter such that the target and the ownvehicle do not collide with each other. Accordingly, the slopes of thestraight lines are corrected according to Equations (6) and (7) tonarrow the width of the collision prediction area along the lateralaxis. Therefore, only targets that are highly likely to collide with theown vehicle are detected. This makes it possible to eliminate the needto determine whether to perform the driving support for the targets thatwill soon be outside the collision prediction area due to accelerationor deceleration of the target or the own vehicle, thereby reducing thefrequency of performing the driving support control.

In Example 2, the slope of the straight line of the right end Xr(t) ofthe collision prediction area and the slope of the straight line of theleft end Xl(t) of the collision prediction area are corrected. In thisregard, both the slopes of the straight lines need not be necessarilycorrected by using the second correction value β. For example, whencorrecting the slope of the straight line of the right end Xr(t) of thecollision prediction area, the first correction value β may be used tonarrow the width of the collision prediction area along the lateralaxis. Meanwhile, the slope of the straight line of the left end Xl(t) ofthe collision prediction area need not be corrected, or may be correctedusing a value different from the second correction value β.

Example 3

In the aforementioned embodiment, the width of the collision predictionarea along the lateral axis is set to the width of the own vehicle. Inthis regard, when the speed of a target along the lateral position axisin the determination plane is lower than the first predetermined speed,in particular, when the target is a pedestrian, it is presumed that thespeed of the target will frequently increase or decrease. In this case,even though it is predicted that the target will be outside thecollision prediction area and pass by the own vehicle, the target maychange the direction to a path of future collision with the own vehicledue to accidental acceleration or deceleration of the target, and mayenter the collision prediction area. In such a situation, when the speedof the target is lower than the first predetermined speed, the collisionprediction unit 15 corrects, as illustrated in FIG. 8, the lateral widthof the collision prediction area to increase to the both sides.Specifically, as described in Equations (8) and (9), the collisionprediction unit 15 corrects the lateral width of the collisionprediction area by multiplying each of the own vehicle front right endXr and the own vehicle front left end Xl, by a first correctioncoefficient γ. The first correction coefficient γ is 1 when the absolutevalue of the speed of the target is higher than the first predeterminedspeed, and tends to be larger than 1 when the absolute value of thespeed of the target becomes lower than the first predetermined speed, asillustrated in FIG. 9(a). This makes it possible to predict a collisionbetween the target and the own vehicle with high accuracy even in thesituation where the behavior of the target is likely to change.

Xr(t)=Xr×γ−V(t)×TTC  (8)

Xl(t)=Xl×γ−V(t)×TTC  (9)

In Example 3, when the speed of the target is lower than the firstpredetermined speed, the collision prediction unit 15 mayincrease/correct the width of the collision prediction area along thelateral position axis. Additionally, the collision prediction unit 15may correct the slopes of the straight lines according to Equations (4)and (5) to widen the collision prediction area in the lateral direction,thereby further increasing the collision prediction area. A specificmethod for correcting the slopes of the straight lines will bedescribed. According to Equation (4), the slope of the straight line ofthe right end Xr(t) of the collision prediction area is corrected bymultiplying the product of the speed of the target and thetime-to-collision, by a value calculated by adding a third correctionvalue Δ to 1. In addition, according to Equation (5), the slope of thestraight line of the left end Xl(t) of the collision prediction area iscorrected by multiplying the product of the speed of the target and thetime-to-collision, by a value calculated by subtracting the thirdcorrection value Δ from 1. The third correction value Δ is 0 when thespeed of the target is higher than the first predetermined speed, andtends to be larger than 0 when the speed of the target becomes lowerthan the first predetermined speed as illustrated in FIG. 6(c). Thismakes it possible to predict a collision between the target and the ownvehicle more reliably with high accuracy in the situation where thebehavior of the target is likely to change.

In Example 3, when the speed of the target is lower than the firstpredetermined speed, the collision prediction unit 15 increases/correctsthe width of the collision prediction area along the lateral positionaxis. In this regard, instead of increasing/correcting the width of thecollision prediction area along the lateral position axis, the collisionprediction unit 15 may correct the slopes of the straight lines correctaccording to Equations (4) and (5) to widen the collision predictionarea in the lateral direction to increase the collision prediction area.

In Example 3, when the speed of the target is lower than the firstpredetermined speed, the collision prediction unit 15 increases/correctsthe width of the collision prediction area along the lateral positionaxis. In this regard, when the relative distance between the target andthe own vehicle is longer than a second predetermined distance, thecollision prediction unit 15 may increase/correct the width of thecollision prediction area along the lateral position axis. Specifically,the collision prediction unit 15 corrects the lateral width of thecollision prediction area by multiplying each of the own vehicle frontright end Xr and the own vehicle front left end Xl, by a secondcorrection coefficient E, according to Equations (8) and (9). The secondcorrection coefficient E is 1 when the relative distance is shorter thanthe second predetermined distance, and tends to be larger than 1 as therelative distance becomes longer than the second predetermined distance,as illustrated in FIG. 9(b)

When the target and the own vehicle are distant from each other, theaccuracy of the information about the target detected by the radardevice 21 becomes low. Accordingly, it may be detected that the targetis not within the collision prediction area due to an error in theinformation about the target, although the target actually is within thecollision prediction area. Therefore, when the relative distance betweenthe target and the own vehicle is longer than the second predetermineddistance, the width of the collision prediction area along the lateralposition axis is increased/corrected. This allows the target to beincluded within the increased/corrected collision prediction area evenif an error has occurred in the information about the target detected bythe radar device 21.

In Example 3, when the speed of the target is lower than the firstpredetermined speed, the collision prediction unit 15 increases/correctsthe width of the collision prediction area along the lateral positionaxis. In this regard, when the relative speed of the target and the ownvehicle is lower than a second predetermined speed, the collisionprediction unit 15 may correct the slopes of the straight lines to widenthe collision prediction area in the lateral direction according toEquations (4) and (5). Specifically, according to Equation (4), thecollision prediction unit 15 corrects the slope of the straight line ofthe right end Xr(t) of the collision prediction area, by multiplying theproduct of the speed of the target and the time-to-collision, by a valuecalculated by adding a fourth correction value to 1. In addition,according to Equation (5), the collision prediction unit 15 corrects theslope of the straight line of the left end Xl(t) of the collisionprediction area by multiplying the product of the speed of the targetand the time-to-collision, by a value calculated by subtracting thefourth correction value from 1. The fourth correction value ζ is 0 whenthe relative speed is higher than the second predetermined speed, andtends to be larger than 0 as the relative speed becomes lower than thesecond predetermined speed, as illustrated in FIG. 6(d).

When the relative speed of the target and the own vehicle is low, anerror might occur in the time-to-collision. In this case, the positionof the target is shifted in the determination plane, and it may bedetected that the target is not within the collision prediction area dueto the error in the calculated time-to-collision, although the targetactually is within the collision prediction area. Therefore, when therelative speed of the target and the own vehicle is lower than thesecond predetermined speed, the collision prediction unit 15 correctsthe slopes of the straight lines to widen the collision prediction areain the lateral direction according to Equations (4) and (5). This allowsthe target to be included within the increased/corrected collisionprediction area even if an error has occurred in the calculatedtime-to-collision in the situation where the speed of the targetrelative to the own vehicle is low.

In Example 3, when the speed of the target is lower than the firstpredetermined speed, the collision prediction unit 15 increases/correctsthe width of the collision prediction area along the lateral positionaxis. In this regard, when the driving support device 100 includes ameans for detecting the turning angular speed of the own vehicle (forexample, a yaw rate sensor), the width of the collision prediction areaalong the lateral position axis may be corrected depending on themagnitude of the curvature radius (curve R) calculated based on theturning angular speed and the speed of the own vehicle. When the curve Ris shorter than a predetermined radius, the collision prediction unit 15corrects the lateral width of the collision prediction area to decreasefrom the both sides, as illustrated in FIG. 10. Specifically, thecollision prediction unit 15 corrects the lateral width of the collisionprediction area by multiplying each of the own vehicle front right endXr and the own vehicle front left end Xl, by a third correctioncoefficient η according to Equations (8) and (9).

The third correction coefficient η is 1 when the curve R is longer thanthe predetermined radius, and tends to be smaller than 1 as the curve Rbecomes shorter than the predetermined radius, as illustrated in FIG.9(c).

When the curve R is shorter than the predetermined radius and the ownvehicle is greatly turning with respect to the traveling direction ofthe own vehicle before the turning, the position of the own vehiclerelative to the target changes substantially. In this case, thecollision prediction area cannot be properly developed and the brakingdevice 32 may be erroneously caused to perform the automatic brakingcontrol. Accordingly, when the curve R is shorter than the predeterminedradius, decreasing and correcting the width of the collision predictionarea along the lateral position axis makes it possible to preventincorrect execution of the automatic braking control by the brakingdevice 32.

In Example 3 and another example applied to Example 3, the lateral widthof the collision prediction area is corrected by multiplying the ownvehicle front right end Xr and the own vehicle front left end Xl, by thesame correction coefficient. In this regard, the own vehicle front rightend Xr and the own vehicle front left end Xl need not necessarily bemultiplied by the same correction coefficient. For example, the ownvehicle front right end Xr may be multiplied by a correctioncoefficient, however the own vehicle front left end Xl may not bemultiplied by the correction coefficient, or may be multiplied by acorrection coefficient different from the correction coefficient used tocorrect the own vehicle front right end Xr.

In still another example applied to Example 3, the slope of the straightline of the right end Xr(t) of the collision prediction area and theslope of the straight line of the left end Xl(t) of the collisionprediction area are corrected using the same correction value. In thisregard, the slopes of the straight lines need not necessarily becorrected using the same correction value. For example, when correctingthe slope of the straight line of the right end Xr(t) of the collisionprediction area, the third correction value Δ or the fourth correctionvalue may be used to widen the collision prediction area in the lateraldirection. Meanwhile, the slope of the straight line of the left endXl(t) of the collision prediction area need not be corrected, or may becorrected using a correction value different from the third correctionvalue Δ or the fourth correction value ζ.

In Example 1, and another example applied to Example 1, Example 2, stillanother example applied to Example 2, Example 3, and still anotherexample applied to Example 3, the coverage of the collision predictionarea is corrected depending on predetermined conditions. The collisionprediction area is an area with a combination of a notification areawhere the warning device 31 performs the notification process and anautomatic braking area where the braking device 32 performs theautomatic braking control. Therefore, the correction controls describedin Example 1, still another example applied to Example 1, Example 2,still another example applied to Example 2, Example 3, and still anotherexample applied to Example 3 are applied to both the notification areaand the automatic braking area. In this regard, different correctioncontrols may be applied to the notification area and the automaticbraking area such as the correction control in Example 1 applied to thenotification area and the correction control in Example 2 applied to theautomatic braking area, for example.

The present disclosure has been described based on embodiments, howeverit should be understood that the present disclosure is not limited tothese embodiments and configurations.

The scope of the present disclosure should encompass variousmodifications or equivalents. Further, various combinations or modes, orother combinations or modes constituted by one or more elements of thevarious combinations or modes are included within the category or ideaof the present disclosure.

PARTIAL REFERENCE SIGNS LIST

-   10 . . . Detection ECU-   21 . . . Radar device-   22 . . . Imaging device

1. A driving support device comprising: a target detection unit thatdetects a target moving in a direction crossing the traveling directionof a vehicle; a collision prediction unit configured to predict acollision between the target detected by the target detection unit andthe vehicle; a support performing unit configured to, when the collisionprediction unit predicts a collision between the target and the vehicle,cause the vehicle to perform driving support for preventing thecollision; a speed calculation unit that calculates the speed of thetarget; a time-to-collision calculation unit configured to calculate atime-to-collision as a prediction time period until the occurrence of acollision between the target and the vehicle based on information aboutthe target detected by the target detection unit; and a both-endsdetection unit that detects both ends of the target detected by thetarget detection unit in a direction orthogonal to the travelingdirection of the vehicle, wherein the collision prediction unitestablishes a collision prediction area as an area in a determinationplane defined by a lateral position axis indicating a lateral positionwith respect to the vehicle in a lateral direction orthogonal to thetraveling direction of the vehicle and a prediction time period axisindicating the time-to-collision set in the traveling direction of thevehicle, and the collision prediction unit predicts a collision with thetarget depending on whether at least a part of a section between theboth ends detected by the both-ends detection unit is within thecollision prediction area, the width of the collision prediction areaalong the lateral position axis is set based on the width of thevehicle, and the lateral position of the collision prediction area isset based on a product calculated by multiplying the speed of the targetby the time-to-collision.
 2. The driving support device according toclaim 1, wherein of the both ends detected by the both-ends detectionunit; an end portion positioned on the left side with respect to thetraveling direction of the vehicle is set as a left end portion and anend portion positioned on the right side with respect to the travelingdirection of the vehicle is set as a right end portion, a left end ofthe collision prediction area along the lateral position axis withrespect to the traveling direction of the vehicle is set as an area leftend and a right end of the collision prediction area along the lateralposition axis with respect to the traveling direction of the vehicle isset as an area right end, and the collision prediction unit predicts acollision with the target when the lateral position of the left endportion of the target is smaller than the lateral position of the arearight end and the lateral position of the right end portion of thetarget is larger than the lateral position of the area left end withrespect to the time-to-collision calculated by the time-to-collisioncalculation unit in the determination plane.
 3. The driving supportdevice according to claim 1, wherein the lateral position of thecollision prediction area is set in the determination plane by straightlines indicating the speed of the target calculated, as slopes, in thedirection of the lateral position axis, by the speed calculation unit,the slopes having a tilt to the prediction time period axis.
 4. Thedriving support device according to claim 3, wherein, when a relativedistance between the vehicle and the target is shorter than a firstpredetermined distance, the collision prediction unit is configured tocorrect slopes of the straight lines to increase a width of thecollision prediction area in the direction of the lateral position axisdepending on the prediction time period axis.
 5. The driving supportdevice according to claim 3, wherein, when the speed of the targetcalculated by the speed calculation unit is lower than a firstpredetermined speed, the collision prediction unit is configured tocorrect slopes of the straight lines to widen the collision predictionarea in the direction of the lateral position axis.
 6. The drivingsupport device according to claim 3, wherein, when the speed of thetarget relative to the vehicle is lower than a second predeterminedspeed, the collision prediction unit is configured to correct slopes ofthe straight lines to widen the collision prediction area in thedirection of the lateral position axis.
 7. The driving support deviceaccording to claim 3, wherein the collision prediction unit correctsslopes of the straight lines to narrow a width of the collisionprediction area in the direction of the lateral position axis in a rangewhere the time-to-collision calculated by the time-to-collisioncalculation unit is longer than a predetermined time.
 8. The drivingsupport device according to claim 1, wherein, when a relative distancebetween the target and the vehicle is longer than a second predetermineddistance, the collision prediction unit increases/corrects a width ofthe collision prediction area along the lateral position axis.
 9. Thedriving support device according to claim 1, wherein, when the speed ofthe target calculated by the speed calculation unit is lower than apredetermined speed, the collision prediction unit increases andcorrects the width of the collision prediction area along the lateralposition axis.
 10. The driving support device according to claim 1,wherein, when the vehicle is turning at an angle larger than apredetermined angle, the collision prediction unit decreases andcorrects the width of the collision prediction area along the lateralposition axis.
 11. The driving support device according to claim 1,wherein the target is a bicycle.
 12. A driving support methodcomprising: a target detection step of detecting a target moving in adirection crossing the traveling direction of a vehicle; a collisionprediction step of predicting a collision between the target detected inthe target detection step and the vehicle; a support performing step of,when a collision between the target and the vehicle is predicted in thecollision prediction step, causing the vehicle to perform drivingsupport for preventing the collision; a speed calculation step ofcalculating the speed of the target; a time-to-collision calculationstep of calculating a time-to-collision as a prediction time perioduntil the occurrence of a collision between the target and the vehiclebased on information about the target detected in the target detectionstep; and a both-ends detection step of detecting both ends of thetarget detected in the target detection step in a direction orthogonalto the traveling direction of the vehicle, wherein in the collisionprediction step, a collision prediction area is established as an areain a determination plane defined by a lateral position axis indicating aposition with respect to the vehicle in a lateral direction orthogonalto the traveling direction of the vehicle and a prediction time periodaxis indicating the time-to-collision set in the traveling direction ofthe vehicle, and a collision with the target is predicted depending onwhether at least a part of a section between the both ends detected inthe both-ends detection step is within the collision prediction area inthe determination plane, the width of the collision prediction areaalong the lateral position axis is set based on the width of thevehicle, and the lateral position of the collision prediction area isset based on a product calculated by multiplying the speed of the targetby the time-to-collision.
 13. The driving support method according toclaim 12, wherein of the both ends detected in the both-ends detectionstep, an end portion positioned on the left side with respect to thetraveling direction of the vehicle is set as left end portion and an endportion positioned on the right side with respect to the travelingdirection of the vehicle is set as right end portion, a left end of thecollision prediction area along the lateral position axis with respectto the traveling direction of the vehicle is set as area left end and aright end of the collision prediction area along the lateral positionaxis with respect to the traveling direction of the vehicle is set asarea right end, and in the collision prediction step, a collision withthe target is predicted when the lateral position of the left endportion of the target is smaller than the lateral position of the arearight end and the lateral position of the right end portion of thetarget is larger than the lateral position of the area left end withrespect to the time-to-collision calculated in the determination planein the time-to-collision calculation step.
 14. The driving supportdevice according to claim 2, wherein the lateral position of thecollision prediction area is set in the determination plane by straightlines indicating the speed of the target calculated, as slopes, in thedirection of the lateral position axis, by the speed calculation unit,the slopes having a tilt to the prediction time period axis.
 15. Thedriving support device according to claim 14, wherein, when a relativedistance between the vehicle and the target is shorter than a firstpredetermined distance, the collision prediction unit is configured tocorrect slopes of the straight lines to increase a width of thecollision prediction area in the direction of the lateral position axisdepending on the prediction time period axis.
 16. The driving supportdevice according to claim 14, wherein, when the speed of the targetcalculated by the speed calculation unit is lower than a firstpredetermined speed, the collision prediction unit is configured tocorrect slopes of the straight lines to widen the collision predictionarea in the direction of the lateral position axis.
 17. The drivingsupport device according to claim 14, wherein, when the speed of thetarget relative to the vehicle is lower than a second predeterminedspeed, the collision prediction unit is configured to correct slopes ofthe straight lines to widen the collision prediction area in thedirection of the lateral position axis.
 18. The driving support deviceaccording to claim 14, wherein the collision prediction unit correctsslopes of the straight lines to narrow a width of the collisionprediction area in the direction of the lateral position axis in a rangewhere the time-to-collision calculated by the time-to-collisioncalculation unit is longer than a predetermined time.
 19. The drivingsupport device according to claim 2, wherein, when a relative distancebetween the target and the vehicle is longer than a second predetermineddistance, the collision prediction unit increases/corrects a width ofthe collision prediction area along the lateral position axis.
 20. Thedriving support device according to claim 2, wherein, when the speed ofthe target calculated by the speed calculation unit is lower than apredetermined speed, the collision prediction unit increases andcorrects the width of the collision prediction area along the lateralposition axis.